Quote from Yngvar
The separation of PvE and PvP will probably upset some people, but I have to admit I love it. I do hope, though, that the PvP enthusiasts will get some more room to play around in. The arena I've seen so far seems a bit small. Especially if the character movement speed will be increased by any considerable amount.
I thought it seemed small at first too, but the reality is you don't want to spend minutes trying to find your opponent. D3 isn't going to be a game of complex preparation tactics - you have to just jump into the fray, and I think that's the message they are trying to keep with small arenas. Even in that small space, it felt like there was plenty of maneuverability for those who were skilled at it. I got kited around many times trying to chase down Wizards